Regardless of your beliefs about the validity or invalidity of the n.o., everyone here hopefully knows not to ever take your phone into the confessional. It can be traced and used against you and the priest, even if it is turned off. If you must carry it inside, you must remove the battery to render it useless for surveillance. My phone remains locked and hidden in my car when in Church. That way, I won't be disturbed or even tempted to have a peek. If it's that important I be immediately reachable, I consider it a valid reason to miss Mass. I do know there are exceptions like medical or emergency personnel, etc. In that case, go to Confession with the battery removed. Hopefully, safe a general Confession for a time you need not be available.